This post for August / Sept., covers photos #12 through # 17, of a Stihl O 28 Wood Boss that came to the shop with an oil leak, general maintenance.
Two defects were present after initial inspection of the unit: (1) black oil from the leak all over power unit, (pic #12) and (2), defective oiler reservoir cap / gasket, that allowed the leak to progress over some years of ownership.
(Pic #12) also shows a pan of black, used auto engine oil I drained from the oiler reservoir; a definite “no-no”, due to combustion impurities contained in the oil, along with what would be left of the additive package. Either of which causes oiler pump / “o” ring / gasket damage.
The oiler reservoir was not completely sealed on the cap end, allowing “chain oil” to leak from the threaded end as well as from the pump side. This defect can be likened unto a soda straw filled with liquid, the straw being the oiler reservoir in this example. When you seal your finger over the top end of the straw, as the oiler reservoir cap should have, nothing flows from the bottom of the straw, until you remove your finger. Since the oiler cap was compromised from deformation, there was no adequate seal to keep the contents in the tank, so oil flowed from under the cap as well as from the pump end. Like removing your finger from the straw. Remembering,that gravity always wins……… well, most of the time.
Remaining photos, demonstrate the importance of complete component cleaning prior to reassembly of the customer’s unit, (pic #13 > pic #17). Of importance, is component separation in pans or other vessels, that will allow organization of each system; ie. starter, ignition, shrouding, fuel / handle systems and related fasteners. This method of organization beats the normal practice of just tossing stuff onto the benchtop, hoping to find “everything” later. I guess what’s left-over could always go into the fuel tank?
After reassembly, there’s always the cutting attachment to service. Bar grooves will be cleaned and a bar groove gauge will measure the inside clearance and rail uniformity. Removal of sawdust from the tailpiece oil holes, along with checking overall straightness. Check the tip for any deformation and lube the sprocket tip both sides if applicable. Then, we sharpen cutters & set the depth controls,(sometimes called rakers), checking for chain “stretch”, that alters chain pitch. Often times “stretch”can be accelerated not only by over tightening / overheating, but also by using improper chain lubricant, such as used engine oil, which is absent adhesive agents that keep the bar and chain lubricated as the chain travels around the bar. Stay tuned and many thanks for stopping by. Be well…….Shade Tree Mechanic.